I’m not a Gmail user but I know someone who is. She was a little disappointed to discover that when configuring her Gmail account with a Microsoft Surface, only one of the many Google calendars synchronised to the built-in Calendar app. It looks like the app only syncs the default calendar. After a little searching, we found a workaround. It’s a little clunky but did the trick. Hopefully this gets fixed properly in an update to the main app.